Relay



E. J. PRATT Oct. 14, 1930.

RELAY Filed Nov. 21, 1928 Patented Got. 14, 1939 PATiEiltT EDWARD J.PRATT, OF NEW? YORK, N. Y.,

FFECE ASSIGNOR BELL TELElI-IONE LABORA- TORIES, INCORPGRATED, OF ITEVJYORK, N. Y... A GORPOEATIGN OF NEW YORK RELAY Application filed November21, 1328.

This invention relates to relays and more particularly to. alternatingcurrent relays for signaling circuits.

It is the object of the invention to provide a relay which is verysensitive, easy to adjust and capable of adjustment for satisfactoryoperation over a wide range of frequencies.

In accordance with the general features of the invention, theserequirements are met by a polarized relay of the tuned reed type inwhich the armature, under the influence of the signaling currents,vibrates between pole faces arranged to provide two fixed and twoworking gaps. An adjustable clamp of magnetic material is adapted tovary the tuning ofthe reed armature and is so arranged with respect tothe magnet system that it serves also to lower the reluctance of thereturn path of the signal flux.

These and other features of the invention will be understood from thefollowing description and the accompanying drawing. In the drawing, Fig.1 represents arelay embodying the invention and shows the coil andpole-pieces in cross section. Fig. 2 is a different view of the relaywhich shows more clearly the novel features of the magnetic circuit, andFig. 3 is a. perspective view with the coil removed to show particularlythe arrangement of the rear pole-pieces and the path of the signal flux.

inasmuch as this invention consists essentially of a novel arrangementof the armature and pole-pieces, the general features of the relay whichare common to all polarized devices of this sort and form no part of thepresent invention, will be described only very briefly.

A permanent magnet 1 for supplying the polarizing flux is attached to arelay base 2 which is in turn supported by brackets 3, 3 and l, 4 to themounting base 5 which is equipped wit-h suitable mounting posts 6. (Sand terminals 7 for adaptingthe relay for use in a standard receptacle.The reed armature 8 is pivoted at one end by a screw 9 and clamped bythe adjustable magnetic clamp 10 which may be moved along the reedarmature to adjust its resonant frequency to the desired value. Theother end of the arma- Serial 1T0. 320,799.

ture is surrounded by a coil 11 which receives the signal currents fromthe external circuit through terminals 7. The members 12 and 13 arearranged to form front pole-pieces above and below the armaturerespectively and the members 1 and 15 are arranged to form rearpole-pieces with faces terminating at the sides of the armature so thatthe reluctance of the gaps will be unchanged as the armature vibrates inresponse to the signal currents. A loosecontact device 16, such as thatdisclosed in Patent 1,628,991, is mounted on the armature in such a waythat its contacts which are connected in the circuit which the relaycontrols, will be opened when the armature vibrates withsuiiicientamplitude. The pole-pieces 12 and 13 are provided withtransverse slots as indicated so that the front gaps 17 and 18 may bemade exactly equal after the armature has been adjusted to the requiredfrequency. Under this condition, a flux will flow from the north to thesouth pole of the magnet through both sets of polepieces, but there willbe no tendency to displace the armature.

Assume then that a signal pulse traverses the coil 11 in such adirection as'to set up'in the armature a flux flowing toward its pivotpoint. Since the rear gaps are very small, say of the order of'.005 ofan inch, this flux will circulate around the magnetic circuit includingthe armature and pole-pieces 15 and 12 as shown by short dashes in Fig.3. Under this condition, the armature no longer will be inequilibriumbut will be deflected upward, since the signal flux opposes thepolarizing flux in gap 18. hen a signal pulse traverses the coil in theopposite direction, the pull between the armature and the pole-piece 13will be decreased in a similar manner so that the armature will bedeflected downward. If these signal pulses occur at substantially thefrequency to which the reed is tuned, the armature will respondsufficiently to operate the loose contact device.

This type of construction employing only two working gaps instead of 4has several advantages over conventional designs. It is found in suchdevices that each time the armature clamp ismoved to niodify the tuningthat the armature becomes slightly biased toward one pole-piece or theother so requireadjustment and these are made readily accessible bymerely removing the relay cover. The rear gaps 1,9 and 20 being ofconstant reluctance regardless of the position of the armature, limitthe flux density which can be built up in that member and thereforeovercome to a large extent the tendency of the armature to stick oneither pole-piece when the relay is being'operated at high sensitivity,that is to say, with very small gaps. This advantage may be utilized ineither of two ways, the workinggaps may be made smaller than would bepractical heretofore, thereby increasing the sensitivity, or the relaymay be used with a greater free length of armature, that is, may betuned to lower frequencies. A relay of the'type described operatesquite' 'satisfactorily with a non-magnetic clampbut it has been foundthat the sensitivity is somewhat further improved by usinga magneticclamp. .While the reason for this has 'notbeen determined definitely, itis believed that'due to the small area of the armature opposite the rearpole-pieces, it has a tendency to become saturated at that point andthat this condition is relieved bylowering the reluctance of the leakagepath between the armature and the permanent magnet. The manner in whichthis is accomplished will be evident from the drawing. The lower portionof the clamp 10 constitutes a low reluctance leakage path extending overthe greater portion of the distance separating the legs of the magnet 1hence while most of the signal flux will I follow the path indicated bythe dotted line 21 in'Figs. 2 and'3 the remainder will flow the armatureto the clamp 10 and through the air to the upper pole of the mag net asindicated by the dotted line 22. Oh viously then this leakage path is inparallel with the fixed air gap 20 so that the leakage flux relieves thesaturation at the sides of the armature but the reluctance of theleakage path is still too high to have any considerab e effect on thestrength of the polarizing flux.

It is understood, of course, that the invention is independent of anytheory of operation and that it is intended to limit it only by thefollowing claims.

' Whatis claimed is:

1. A magnetic circuit for electromagnetic devices comprising a reed typearmature and amagnet having two sets of pole faces at 'right angles toeach other and adjacent to the armature.

' 2. A magnetic circuit for electromagnetic devices comprising a reedtype armature secured by a magnetic clamp and a magnet having two setsof pole faces at right angles to each other and adjacent to thearmature, the magnetic clamp forming part of a return circuit for theflux of the magnet.

3. An electromagnetic device comprising a magnet'having two north andtwo south relation to the magnetic circuit and the magnetic circuitcomprising a reed type armature, an adjustable clamping device so curingthe armature and a magnet with poles bifurcated to form air-gaps withthe armature, two of the gaps being independent of the clamping noviceand of substantially constant reluctance for all working positions ofthe armature;

In witness whereof, I hereunto subscribe my name this 20th day ofNovember, 1928; EDWARD J. PBATTL,

